A goniometer is an instrument for measuring angles. Goniometers are known for use in medicine for measuring the relative angles of various anatomical points.
U.S. Pat. No. 229,372 discloses a goniometer for measuring angular movement of joints between bones in a human body. The goniometer comprises a protractor head having an arcuate sector with an angle indicating scale. The ends of the arcuate sector are joined to an elongated base section arranged to be aligned with a body part, for instance the upper leg, with the centre of the arcuate section aligned with a joint, for instance the knee. A pointing arm is rotatably coupled to the base section at the centre of the arcuate section and is arranged to be aligned with a second body part, for instance the lower leg. The position of the pointing arm relative to the arcuate section is indicative of the angle of the joint.
US-2007/0266579-A1 discloses a similar goniometer for performing range of motion measurements upon a human patient.
During orthopedic surgery it is a common requirement to be able to align surgical instruments, such as a drill guide, or a prosthesis with a body axis, or at a predetermined angle relative to the body axis. Commonly, the correct alignment of the instrument or the prosthesis is dependent upon visual inspection and the skill of the surgeon.
It is an object of embodiments of the present invention to obviate or mitigate one or more of the problems of the prior art, whether identified herein or elsewhere.